Hairpin Windings for Traction Machines: Analysis and Comparison

This work investigates circulating currents and additional losses in hairpin windings with multiple parallel paths when a weak symmetry pattern is adopted. The theoretical rules for designing hairpin windings may lead to configurations not completely preventing parasitic currents in the parallel branches, especially in heavy saturation conditions. Often, the proposed configurations in the literature present a weak symmetry between the parallel branches. This paper considers a typical hairpin winding configuration to compute the actual currents in the parallel paths. For this purpose, machine models are driven by an external three-phase circuit and finite element analyses are carried out. The main goal is to explain the causes of circulating currents. The analysis is repeated using different rotor topologies and keeping respectively the same stator design, overall machine volume and hairpin winding pattern to look into the different effects in windings induced by parasitic currents.